As more and more challenging conditions are encountered in oilfield drilling operations, there is a need for high-performance rheology modifiers used in water-based drilling fluids. The enhanced performance of the drilling fluids, especially, the High-Temperature-High-Pressure (HTHP) compatibility will allow faster and safer drilling operations. A rheology modifier is a critical component in water-based drilling fluids to ensure a proper rheology profile which performs specific functions such as suspending weighting agents and hole-cleaning. Xanthan Gum is the most commonly used rheology modifier in water-based drilling fluids. The xanthan gum was known to start losing rheological properties at above 300° F., so it is not suitable for HTHP based drilling operations. Therefore, a desired rheology modifier should possess similar rheological properties, for example, highly shear thinning with enhanced thermal stability. These enhanced properties will allow successful drilling operations under HTHP conditions. Therefore, the development of such HTHP based rheology modifier is critically important to the oil and energy based industries where drilling plays a vital role. The HTHP compatible water-based drilling fluid will allow more environmental friendly drilling operations in a safe and efficient manner. Therefore, without a high performance rheology modifier, such drilling operations under HTHP conditions are extremely challenging.
U.S. Pat. No. 7,205,271 assigned to ISP Investments Inc. discloses a rheology modifier/hair styling resin consisting of a crosslinked, linear poly(vinyl amide/polymerizable carboxylic acid) copolymer having a composition, by weight, of 25 to 75% of a vinyl amide monomer selected from vinyl pyrrolidone, vinyl caprolactam, N-vinyl formamide, N-vinylacetamide, N-vinyl-N-methylacetamide and mixtures thereof, and 25 to 75% of a polymerizable carboxylic acid monomer selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid and mixtures thereof, and a crosslinker in an amount of 0.5 to 2% based on weight of total monomers, which is characterized by an aqueous solution having a viscosity of 55,000 cps at a pH of 9 (Brookfield RVT, T-bar C@ 10 RPM, 60 sec., 1% resin solids in water).
US Publication No. 20110218295 assigned to BASF SE discloses a new anionic associative rheology modifiers comprising as polymerized units (a) 25 to 85% by weight of acrylic acid (AA), (b) 10 to 60% by weight of N-vinyl pyrrolidone (VP), (c) 0.5 to 10% by weight of at least one cationic monomer, (d) 1 to 6% by weight of at least one of compounds (d1) or (d2).

U.S. Pat. No. 5,211,858 assigned to Union Oil Company of California discloses a method for inhibiting the migration of a hazardous acid plume through a subterranean stratum, the method comprising the step of injecting into at least a portion of the acid plume a slug of a composition capable of forming a gel, the composition comprising: (a) a crosslinkable polymer; and (b) a lanthanide, wherein the crosslinkable polymer is selected from the group consisting of polyacrylamide and copolymers of acrylamide and (A) acrylic acid (B) Vinylpyrrolidone, (C) sodium 2-acrylamido-2-methylpropane sulfonate, and (D) mixtures of (A), (B), and (C).
U.S. Pat. No. 5,393,810A assigned to Halliburton Company disclose a compositions and methods which provide improved viscosity reduction of crosslinked hydratable polymer treating fluids in the presence of uncured resin-coated proppants. The uncured resins are generally uncured phenolic or furan resins. The breaker comprises an oxidizing agent to which is added a sequestering agent comprising a copolymer of vinylpyrrolidone and acrylic acid to sequester at least a portion of any phenolic extracts from said resin that may be present in said treating fluid from contact with the uncured resin.
US Publication No. 20080193395 assigned to BEIERSDORF AG disclose a cosmetic preparation containing (a) one or more water-soluble UV photo protective filters selected from the group of the compounds 2-phenylbenzimidazole-5-sulfonic acid and the sodium, potassium and triethanolammonium salts thereof as well as phenylene-1,4-bis-(2-benzimidazyl)-3,3′-5,5′-tetrasulfonic acid and the sodium, potassium and triethanolammonium salts thereof, (b) a copolymer of vinylpyrrolidone (VP) and acrylic acid (AA).
In view of the foregoing, it is an object of the present application to provide high performance rheology modifiers which is (i) capable retaining its original rheological properties even at high temperatures i.e. beyond 300° F.; (ii) compatible for water based oil field drilling operations under HTHP conditions; and (iii) capable to providing highly shear thinning property with enhanced thermal stability.
Surprisingly, we have found that the use of crosslinked, linear poly(vinyl amide/polymerizable carboxylic acid) copolymer is able to provide required high performance rheological properties which are suitable for HTHP water based oil-well servicing fluids. Such copolymer may be used alone or in combination with other at least one HTHP or Non-HTHP based Rheology Modifiers (RMs), Fluid Loss Additives (FLA's) and/or dispersants that are known in the prior arts.